The most common method for the production of cyanoacrylate monomers involves the base catalyzed Knoevenagel condensation of cyanoacetate with formaldehyde, followed by acid catalyzed thermolysis of the intermediate polymer. This method is exemplified in many references, for instance U.S. Pat. Nos, 2,721,858; 3,254,111; 3,355,482; 3,654,340; 5,140,084 and 5,359,101. This method is effective and inexpensive in producing low molecular weight monomers, but as the size of the cyanoacrylate ester increases the method becomes more difficult and yields diminish substantially. Cyanoacrylate esters of monofunctional C.sub.8 or higher aliphatic alcohols cannot be produced in commercially practical yields by this method.
There are several other synthetic methods known for producing cyanoacrylates including:
Diels-Alder protection/deprotection as exemplified by U.S. Pat. No. 3,463,804 and 4,012,402;
transesterification of cyanoacrylate monomers with alcohols as reported in WPI 80-82239C/46, abstracting (SU 726086 (1980)); PA1 direct esterification of cyanoacrylic acid with alcohols as reported in DE 34 15 181 (1984); PA1 thermal decomposition of alkyl 2-cyano-3-alkoxypropionates and the 3-acyloxy analogs, reported in U.S. Pat. No. 2,467,926; and PA1 pyrolysis of the cyanohydrin acetates of pyruvic acid esters, reported in U.S. Pat. No. 2,391,251. PA1 preparing a compound which is an .alpha.-selenoaryl-.alpha.-cyanopropionate ester of said alcohol, PA1 oxidizing said .alpha.-selenoaryl-.alpha.-cyanopropionate ester to the corresponding selenoxide, PA1 eliminating arylselenic acid from said selenoxide to produce said .alpha.-cyanoacrylate ester, and PA1 separating said .alpha.-cyanoacrylate ester from said arylselenic acid.
Monomers having a plurality of cyanoacrylate groups per molecule are particularly desirable because they can give crosslinked products on polymerization, alone or in combination with conventional monofunctional cyanoacrylate monomers. Crosslinked polymers give improved properties such as solvent resistance. The Diels-Alder protection/deprotection disclosed in U.S. Pat. No. 4,012,402 has been used to prepare various bis-cyanoacrylate monomers. However, the method is cumbersome and not suited to commercial production.
Kadykov, et. al., "Synthesis and Properties of Siloxane Cyanoacrylate Adhesives," Plast. massy, 1984, No. 10, pp.8-9, reports an alleged syntheses of "diacryl-.alpha.-cyano-.beta.-hydroxypropyldimethylsiloxane" by reaction of one mole diepoxydimethylsiloxane and two moles .alpha.-cyanoacrylic acid in the presence of 0.03 moles tertiary amine catalyst and 0.05 mole hydroquinone monomethyl ether. The reaction is reported to be exothermic and to produce the bis-ester of the formula: ##STR1##
However, the reaction conditions employed make it unlikely that such a product could actually be isolated and the analytical data reported in this reference on the product which was isolated is believed to confirm that the product was not the bis-cyanoacrylate.
There therefore exists a need for further alternative methods for cyanoacrylate ester production and in particular methods which can be used for production of monomers having plural cyanoacrylate functionality in reasonable yield and with less difficulty than that of U.S. Pat. No. 4,012,402.
In Reich, et al, JACS, 97, 5434-47 (1975) and Bucheister, et al, Organometallics, 1, 1679-84 (1982), it is reported that certain .alpha..beta.-unsaturated methyl or ethyl esters were prepared by oxidation/elimination reactions performed on corresponding methyl or ethyl .alpha.-selenoarylpropionate esters. However it has not been previously proposed or suggested to try to use such procedure to prepare .alpha.-cyanoacrylate esters, nor has it been proposed or suggested to try to prepare esters of C.sub.8 or higher alcohols or plural ester compounds by preparation and oxidation/elimination of .alpha.-selenoaryl-.alpha.-cyanopropionate esters.